Lidar system with improved scanning speed for high-resolution depth mapping

ABSTRACT

A lidar system can include a light source that emits a pulse of light and a splitter that splits the pulse of light into two or more pulses of angularly separated light. The lidar system can also include a scanner configured to scan pulses of light along a scanning direction across a plurality of pixels located downrange from the lidar system. The lidar system can also include a detector array with a first detector and a second detector. The first and second detectors can be separated by a detector-separation distance along a direction corresponding to the scanning direction of the light pulses. The first detector can be configured to detect scattered light from the first pulse of light and the second detector can be configured to detect scattered light from the second pulse of light.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference under 37 CFR 1.57. Forexample, this application claims priority to U.S. Provisional PatentApplication No. 62/251,672, filed Nov. 5, 2015, and entitled “LIDARSYSTEM WITH IMPROVED SCANNING SPEED FOR HIGH-RESOLUTION DEPTH MAPPING,”the entirety of which is hereby incorporated by reference herein.

BACKGROUND OF THE INVENTION

Field of the Invention

This disclosure relates to scanning lidar systems for creating a depthmap of a field of regard.

Description of the Related Art

Lidar is a technology that can be used to measure distances to remotetargets. Typically, a lidar system includes a light source and adetector. The light source emits light pulses toward a target which thenscatters the light. Some of the scattered light is received back at thedetector. The system determines the distance to the target based on oneor more characteristics associated with the returned light pulses. Forexample, the system may determine the distance to the target based onthe time of flight of a returned light pulse.

SUMMARY

In some embodiments, a lidar system comprises: a light source configuredto emit a pulse of light; a splitter configured to split the emittedpulse of light into two or more pulses of angularly separated lightcomprising a first pulse of light and a second pulse of light; a scannerconfigured to scan pulses of light, which are emitted by the lightsource and split by the splitter, along a scanning direction across aplurality of pixels located downrange from the lidar system; and adetector array comprising a first detector and a second detector,wherein: the first and second detectors are separated by adetector-separation distance along a direction corresponding to thescanning direction of the light pulses; the first detector is configuredto detect scattered light from the first pulse of light; and the seconddetector is configured to detect scattered light from the second pulseof light.

In some embodiments, a method comprises: emitting, by a light source ofa lidar system, a pulse of light; splitting, by a splitter, the emittedpulse of light into two or more pulses of angularly separated lightcomprising a first pulse of light and a second pulse of light; scanningpulses of light, which are emitted by the light source and split by thesplitter, along a scanning direction across a plurality of pixelslocated downrange from the lidar system; detecting, by a first detectorof a detector array, scattered light from the first pulse of light,wherein the detector array comprises the first detector and a seconddetector, wherein the first and second detectors are separated by adetector-separation distance along a direction corresponding to thescanning direction of the light pulses; and detecting, by the seconddetector of the detector array, scattered light from the second pulse oflight.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a lidar system 100 capable of improved scanning speedfor high-resolution depth mapping.

FIG. 2 illustrates the spatial relationship between a downrange pixeland the field of view of the first detector 130 a at a scan time whichcorresponds to a close range target in pixel #1.

FIG. 3 illustrates the spatial relationship between a downrange pixeland the field of view of the first detector 130 a at a scan time whichcorresponds to a midrange target in pixel #1.

FIG. 4 illustrates the spatial relationship between a downrange pixeland the field of view of the first detector 130 a at a scan time whichcorresponds to a maximum range target in pixel #1.

FIG. 5 illustrates the spatial relationship between a downrange pixeland the field of view of the first detector 130 a at a scan time whichcorresponds to a 2× maximum range target in pixel #1.

FIG. 6 is a diagram which shows which pixels are detected togetherduring various ranging periods.

FIG. 7 is a diagram which shows which pixels are detected in eachscanning line over time.

FIG. 8 is a diagram of a detector array 128 which includes detectors 130a-f spaced apart in two dimensions for simultaneously scanning multiplerows in the field of regard.

FIG. 9 illustrates the spatial relationship between a downrange pixeland the field of view of a detector, where the detector field of view islarger than the pixel.

FIG. 10 is a diagram of a detector array which includes two detectors.

FIG. 11 illustrates forward and reverse scans based on the detectorarray in FIG. 10.

FIG. 12 is a diagram of a detector array which includes three detectors.

FIG. 13 illustrates forward and reverse scans based on the detectorarray in FIG. 12.

FIG. 14 illustrates an example method for detecting light scattered by atarget.

FIG. 15 illustrates an example method for detecting scattered light fromangularly separated pulses of light.

DETAILED DESCRIPTION

Lidar systems can be used to determine the distance to a downrangetarget. By scanning the lidar system across a field of regard, thesystem can be used to map the distance to a number of points within thefield of regard. Each of these points can be referred to as a pixel. Itis often desirable that the depth-mapped points within the field ofregard be as closely spaced as possible in order to achieve a highresolution depth map of the field of regard. In addition, it is oftendesirable that the scan time required to create the depth map be asshort as possible. For example, it may be desirable to repeatedlycomplete depth maps of the field of regard at frame rates fast enough tosupport a depth map video (e.g., 30 frames per second). This disclosuredescribes a lidar system 100 which is capable of achieving relativelyhigh resolution depth maps at video frame rates.

FIG. 1 illustrates a lidar system 100 capable of improved scanning speedfor high-resolution depth mapping. The lidar system 100 includes a lightsource 110. The light source can be, for example, a pulsed laser. Thelight source 110 emits a pulse of light which propagates toward acollimating lens 112. After passing through the collimating lens 112,the pulse of light is transmitted directly through a beam splitter 114toward a quarter wave plate 116. The pulse of light then reflects from ascanner 118. The scanner 118 can be, for example, a scanning mirror 118that rotates around at least one axis in order to direct light pulsesacross the field of regard. As an example, the scanner 118 can include agalvanometer scanner, a resonant scanner, a voice coil motor, a DCmotor, a stepper motor, or a microelectromechanical systems (MEMS)device. In some embodiments, instead of a beam splitter 114 and quarterwave plate 116, the lidar system 100 may include a mirror configured sothat a pulse of light emitted by the light source 110 passes through themirror. As an example, the mirror may include a hole, slot, or otheraperture that the pulse of light passes through as it travels to thescanning mirror 118. Light that is scattered by the target 122 maypropagate back toward the lidar system, and the mirror may reflect thisreturn light toward mirror 124 which then directs the light towarddetector lens 126. Other physical layouts and combinations of opticalelements can also be used.

After reflecting from the scanner 118, the pulse of light is incidentupon a holographic element, pixelator, diffractive element, or similardevice 120. The holographic element or pixelator 120 splits the pulse oflight into two pulses which now travel along separateangularly-separated paths 140, 141. The two pulses of light propagatedownrange from the lidar system 100 toward a target 122. In FIG. 1, thetarget 122 is illustrated as being located at the maximum range of thelidar system 100.

In some embodiments, the angular separation θ imparted by theholographic element or pixelator 120 is such that the distance betweenthe two light pulses at the maximum range of the lidar systemcorresponds to the width of multiple pixels. For example, theholographic element or pixelator can be designed such that theseparation between the two light pulses at the maximum range correspondsto an odd number of pixels greater than or equal to three pixels (e.g.,3, 5, 7, 9, etc.). (The significance of this particular spacing isdescribed below.) In FIG. 1, four pixels are labeled on the target 122.One of the light pulses is directed to the first pixel, while the otherlight pulse is directed to the fourth pixel. Thus, the spacing betweenthe light pulses is three pixels in this embodiment.

The light pulses scatter from the target 122 and a portion of each pulsepropagates back toward the lidar system along reciprocal paths 140, 141.Each return light pulse is reflected by the scanner 118, which has sincerotated slightly from its position when the pulses were transmitted,toward the quarter wave plate 116. After passing through the quarterwave plate 116, the return light pulses are reflected by the beamsplitter 114 toward a mirror 124. (Although FIG. 1 illustrates that thelight source 110 and the detector array 128 share an aperture via thebeam splitter 114, other embodiments are possible without a sharedaperture.) The mirror 124 reflects the return light pulses toward adetector lens 126, the detector lens 126 focuses the return light pulseson a detector array 128 located at the focal plane of the lens 126. Asdiscussed further herein, the detector focal plane array 128 includes atleast two spatially-separated detectors 130 a, 130 b. The separationbetween the two detectors 130 a, 130 b is in the scanning dimension ofthe lidar system 100. As shown in FIG. 1, the return light pulse frompixel #1 is focused on the first detector 130 a, while the return lightpulse from pixel #4 is focused on the second detector 130 b. Thus, theseparation between the two detectors 130 a, 130 b corresponds to thespacing between the light pulses at the maximum range of the lidarsystem 100. Consequently, the separation between the detectors 130 a,130 b likewise corresponds to the spacing between an odd number ofpixels greater than or equal to three. (Once again, the significance ofthis spacing is discussed below.)

The detectors 130 a, 130 b create electrical signals which areindicative of the return light pulses. The electrical signals are fed toa processor 132 which then determines the distance to the target 122based on, for example, the time of flight of the light pulses. Thisprocess is repeated as the scanner 118 traverses the field of regard inorder to create a depth map of the scene. The processor 132 can also beused to control the timing of light pulses from the light source 110 andother functions of the lidar system 100.

FIG. 2 illustrates the spatial relationship between a downrange pixeland the field of view of the first detector 130 a at a scan time whichcorresponds to a close range target in pixel #1. The size of the pixeldepends on the size of the angular field of view of the light source 110and the distance to the downrange target 122. In some embodiments, thelight source 110 has an angular field of view on the order ofmilliradians, though it could be larger or smaller depending upon theapplication. In some embodiments, the angular field of view of eachdetector 130 a, 130 b is substantially equal to that of the light source110, though this is not necessarily required. As illustrated, though, inFIG. 2, the pixel and the detector field of view have the same size.

The lidar system 100 is designed such that each detector 130 a, 130 b isaligned with a downrange pixel that is respectively offset from one ofthe downrange pixels with which the light source 110 is aligned (thelight source 110 is aligned with two downrange pixels simultaneouslybecause of the pixelator 120). For example, in some embodiments, thedetectors 130 a, 130 b are aimed at the two pixels directly adjacent (inthe direction opposite the scanning direction) to the respectivedownrange pixels with which the light source is aligned.

With reference to FIG. 2, the light source 110 emits a pulse of light ata time t₁ when the scanner 118 is positioned so as to direct the firstpulse toward pixel #1 (and the second pulse toward pixel #4). Thescanner 118 continues to scan (left to right) to the next pixel afterthe pulse of light is emitted (and subsequently split into two pulses).Because the field of view of the first detector 130 a is offset fromthat of the light source in the direction opposite the scanningdirection, the field of view of the first detector 130 a does not alignwith pixel #1 until a subsequent time after t₁.

In FIG. 2, a relatively short period of time has passed since the lightpulse was emitted. Therefore, the field of view of the detector 130 aslightly overlaps pixel #1. If a return pulse were received by thedetector 130 a at the time illustrated in FIG. 2, then the processor 132would register detection of a close range target 122 owing to the shortelapsed time of flight. Although the detector field of view onlypartially overlaps with pixel #1 in the case of a close range target,the return pulse is still strong enough to be detected because the 1/r̂2signal loss is small owing to the relatively close range of the target.

FIG. 3 illustrates the spatial relationship between a downrange pixeland the field of view of the first detector 130 a at a scan time whichcorresponds to a midrange target in pixel #1. At this scan time, thefield of view of the detector 130 a overlaps pixel #1 by a greateramount than was the case for the short-range target in FIG. 2. This isdue to the greater elapsed scanning time since t₁. Because of thegreater overlap between the field of view of the detector 130 a andpixel #1, the greater 1/r̂2 signal loss resulting from a more distanttarget is at least partially offset. The detector 130 a is thereforeable to detect the return pulse from the midrange target.

FIG. 4 illustrates the spatial relationship between a downrange pixeland the field of view of the first detector 130 a at a scan time whichcorresponds to a maximum range target in pixel #1. As illustrated byFIG. 4, the scanning speed of the scanner 118 can be set such that thefield of view of the first detector 130 a substantially completelyoverlaps pixel #1 at a scan time which corresponds to the round-triptime for a target 122 located at the maximum range of the lidar system100. (In other words, in the case of the illustrated example, the timerequired for the scanner to move the width of one pixel is about thesame as the round trip time for the maximum range of the system 100; thetime to completely traverse one pixel from one side to the other isabout 2× the round trip time for the maximum range.) It is advantageousfor the field of view of the detector to substantially completelyoverlap pixel #1 for a maximum range target in order to at leastpartially offset the greater 1/r̂2 signal loss which results from theround-trip propagation distance associated with the maximum range of thelidar system.

A comparison of FIG. 4 with FIG. 2 reveals that, at a scan timecorresponding to a maximum range target for pixel #1, the detector fieldof view is in the same position relative to pixel #2 as it was relativeto pixel #1 when the scan of pixel #1 began. This might suggest that thedetector can begin scanning pixel #2 at this time. The problem withdoing so, however, is that a target located in pixel #1 just beyond themaximum range of the lidar system 100 could be confused for ashort-range target located in pixel #2. One way to avoid this ambiguitywould be to pause or reduce the scanning speed of the scanner 118.Another way to avoid the ambiguity would be to decrease the scanningresolution. However, neither of these solutions is particularlydesirable. The lidar system 100 illustrated in FIG. 1 instead uses abetter solution.

As shown in FIG. 1, the detector array 128 includes twospatially-separated detectors 130 a, 130 b. And, as already discussed,the two detectors 130 a, 130 b are offset from one another in thescanning direction by a distance which corresponds to an odd number ofpixels greater than or equal to three. Specifically, in FIG. 1, thedetectors are offset from one another by a distance corresponding tothree pixels. Thus, when the first detector 130 a is aligned with pixel#1, the second detector 130 b is aligned with pixel #4. Furthermore,because of the presence of the holographic element or pixelator 120,when a pulse of light is emitted toward pixel #1, another pulse of lightis also emitted toward pixel #4. This means that pixel #1 and pixel #4can be simultaneously detected by the two detectors 130 a, 130 b.

As just discussed above with respect to FIG. 4, there are disadvantagesassociated with beginning to scan pixel #2 when the scanner 118 is inposition for the first detector 130 a to do so. For the same reasons,there are also disadvantages associated with beginning to scan pixel #5when the scanner is in position for the second detector 130 b to do so.This is because of the risk of misidentifying distant targets—beyond themaximum range of the system—located in pixels #1 and #4 as short-rangetargets located in pixels #2 and #5, respectively. This risk can bealleviated by skipping pixel #2 and pixel #5 at this time (i.e., notemitting laser pulses toward these pixels at this time) and insteadwaiting until the scanner 118 is in position for the first detector 130a to scan pixel #3 and the second detector 130 b to scan pixel #6. Thisis illustrated in FIG. 5.

FIG. 5 illustrates the spatial relationship between a downrange pixeland the field of view of the first detector 130 a at a scan time whichcorresponds to a 2× maximum range target in pixel #1. At this scanningposition, there is a diminished risk of falsely detecting a target inpixel #1 because such a target would be located at twice the maximumrange of the system and a return light pulse would incur a relativelylarge amount of 1/r̂2 loss associated with that distance. The signalassociated with any such return would possibly not rise above the noisefloor of the system. (Nevertheless, if the risk of misidentifying therange of a target in a pixel is deemed too great even at a distance of2× the maximum range of the system, then the first and second detectors130 a, 130 b can instead be separated by a distance which corresponds to5, 7, 9, etc. pixels.) At the scanning position illustrated in FIG. 5,the first detector 130 a is in position to begin scanning pixel #3.Though not illustrated, the second detector 130 b would similarly be inposition to begin scanning pixel #6. Thus, the processor 132 can causethe light source 110 to emit a pulse of light at the scanner position.As already discussed herein, the pulse of light is divided by theholographic element or pixelator 120 so as to cause pulses to be senttoward both pixel #3 and pixel #6 at the same time. These pixels arethen ranged by the detectors 130 a, 130 b (in the same mannerillustrated in FIGS. 2-4) as the scanner 118 continues its progressacross the field of regard.

FIG. 6 is a diagram which shows which pixels are detected togetherduring various ranging periods. Pixels which are detected in aparticular ranging period are indicated in FIG. 6 with stars, whilepixels which are not detected during that ranging period are crossed outor are not shown. As already discussed herein, in some embodiments, thefirst and second detectors 130 a, 130 b are spatially separated suchthat they are in position to simultaneously range/detect pixels whichare spaced apart in the scan direction by three pixels. Thus, during thefirst ranging period, pixels #1 and #4 are detected. During the secondranging period, pixels #3 and #6 are detected. During the third rangingperiod, pixels #5 and #8 are detected, and so on. In this way, the firstdetector 130 a detects odd pixels, while the second detector 130 bdetects even pixels.

FIG. 7 is a diagram which shows which pixels are detected in eachscanning line over time. As shown in the diagram, every pixel in thescanning line is detected with the exception of pixel #2. In manyapplications, this trade-off will be acceptable in order to achievehigher scanning speeds and increased resolution. However, if it isnecessary to scan every pixel in the line, then the scanner 118 can beconfigured to scan one or more additional pixels at the tail end of theline in order to compensate.

FIG. 8 is a diagram of a detector array 128 which includes detectors 130a-f spaced apart in two dimensions for simultaneously scanning multiplerows in the field of regard. Each row of detectors in the detector array128 can scan a line in the field of regard at the same time. Asillustrated, detectors 130 a and 130 b can scan line #1 in the manneralready discussed herein. Simultaneously, detectors 130 c and 130 d canscan line #5 and detectors 130 e and 130 f can scan line #9. By spacingthe detectors out in the vertical axis, the scanner can simply reversedirection and move the line of sight down one line to achieve the scan.Otherwise, the scan would be delayed by the time the vertical portion ofthe scan traverses the number of detector lines before the next scanline(s) are initiated. However, other arrangements and spacings betweenthe detectors in the direction perpendicular to the scanning directionare also possible.

In some embodiments, a lidar system 100 may include a light source 110,a scanner 118, and a detector (e.g., detector 130 a). The scanner 118may be configured to scan a field of view of the light source 110 in ascanning direction across multiple pixels (e.g., pixels #1-#3illustrated in FIGS. 1-5 or pixels #1-#8 illustrated in FIGS. 6-7)located downrange from the lidar system. The pixels may include pixel #1and pixel #2, where pixel #2 is located adjacent to pixel #1 along thescanning direction. Pixel #2 being located adjacent to pixel #1 alongthe scanning direction may indicate that the light-source field of viewbegins to scan across pixel #1 prior to scanning across pixel #2 (i.e.,pixel #1 is scanned before pixel #2). As an example, if the scanningdirection is from left to right (e.g., as indicated in FIGS. 2-5), thenpixel #2 is located to the right of pixel #1. The scanning directionindicated in FIGS. 2-5 (e.g., from left to right) may be referred to asa forward-scanning direction, and a direction that is substantiallyopposite the forward-scanning direction (e.g., from right to left) maybe referred to as a reverse-scanning direction.

In some embodiments, a pixel may represent or may correspond to a fieldof view of the light source 110. As the light-source beam propagatesaway from the light source 110, the diameter of the beam (as well as thesize of a corresponding pixel) may increase according to the beamdivergence. As an example, if the light source 110 has a divergence of 1milliradian (mrad), then at a distance of 100 m from the light source110, the light-source beam may have a size or diameter of approximately10 cm, and a corresponding pixel may also have a corresponding size ordiameter of approximately 10 cm. At a distance of 200 m from the lightsource 110, the light-source beam and the corresponding pixel may eachhave a diameter of approximately 20 cm.

In some embodiments, the light source 110 may emit a pulse of light at atime t₁, and the scanner 118 may direct the pulse of light toward pixel#2 (e.g., when the pulse is emitted, the light-source field of view maypartially, substantially, or completely overlap pixel #2). The scanner118 may also be configured to scan a field of view of detector 130 aacross the pixels in the same scanning direction as the light-sourcefield of view is scanned. In some embodiments, the detector 130 a fieldof view may be offset from the light-source field of view in a directionopposite the scanning direction (e.g., the field of view of detector 130a lags behind the light-source field of view). The offset between thedetector and light-source fields of view may be such that, at time t₁when the pulse is emitted, the field of view of detector 130 a at leastpartially overlaps pixel #1, and the light-source field of view at leastpartially overlaps pixel #2 (e.g., the field of view of detector 130 alags behind the light-source field of view by approximately one pixel).As an example, at time t₁, the field of view of detector 130 a mayoverlap substantially all (e.g., greater than or equal to 80%) of pixel#1 (e.g., as illustrated in FIG. 4), and the light-source field of viewmay overlap substantially all (e.g., greater than or equal to 80%) ofpixel #2. Additionally, at time t₁, the field of view of detector 130 amay overlap less than 10% of pixel #2, and the light-source field ofview may overlap less than 10% of pixel #1. The detector field of viewmay be any suitable size relative to the light-source field of view. Asan example, the angular size of the detector field of view may besmaller than, substantially the same size as, or larger than the angularsize of the light-source field of view.

In some embodiments, detector 130 a may be configured to detect aportion of the pulse of light which is scattered by a target located atleast partially within pixel #2. The portion of the pulse of light maybe detected at any suitable time after t₁ when the pulse is emitted(e.g., detector 130 a may detect the portion of the pulse at a time t₂,where t₂>t₁). In some embodiments, lidar system 100 may include aprocessor 132 which determines a distance from the lidar system 100 tothe target based at least in part on a time of flight of the pulse oflight, where the time of flight is (t₂−t₁). If lidar system 100 measuresa time of flight of Δt (e.g., Δt, which equals t₂−t₁, represents theround-trip time for light to travel from the lidar system 100 to atarget and back to the lidar system 100), then the distance D from thetarget to the lidar system 100 may be expressed as D=c·Δt/2, where c isthe speed of light (approximately 3.0×10⁸ m/s). As an example, if a timeof flight is measured to be Δt=300 ns, then the distance from the target122 to the lidar system 100 is approximately D=45.0 m.

If the distance from the lidar system 100 to the target 122 correspondsto a maximum range of the lidar system 100, then a round-trip timecorresponding to the maximum range of the lidar system is approximately(t₂−t₁), and at time t₂ (when the detector detects the scattered portionof the emitted pulse) the field of view of detector 130 a overlapssubstantially all (e.g., greater than or equal to 80%) of pixel #2. Themaximum range of lidar system 100 may be any suitable distance, such asfor example, 100 m, 200 m, 500 m, or 1 km. As an example, if the maximumrange is 200 m, then the time of flight corresponding to the maximumrange is approximately 2·(200 m)/c≅1.33 μs. In some embodiments, if thetarget is a close-range target located within 20% of the maximum rangeof the lidar system 100, then at time t₂ (when the detector detects thescattered portion of the emitted pulse) the detector field of view mayoverlap less than or equal to 20% of pixel #2. In some embodiments, ifthe target is a midrange target located between 20% and 80% of themaximum range of the lidar system 100, then at time t₂ the detectorfield of view may overlap between 20% and 80% of pixel #2. In someembodiments, if the target is located a distance greater than or equalto 80% of the maximum range of the lidar system 100, then at time t₂ thedetector field of view may overlap greater than or equal to 80% of pixel#2.

In some embodiments, the field of view of detector 130 a and thelight-source field of view may have approximately the same scanningspeed. As an example, the detector field of view and the light-sourcefield of view may each scan a width of one pixel in a time that isapproximately equal to the round-trip time corresponding to the maximumrange of the lidar system 100. In some embodiments, the detector fieldof view being offset from the light-source field of view in thedirection opposite the scanning direction may result in the detectorfield of view being aligned with pixel #2 at a time t₃, where t₃ isgreater than t₁, t₃ is greater than or equal to t₂, and (t₃−t₁)corresponds to the round-trip time for the maximum range of the lidarsystem 100. As an example, the light source may emit a pulse of lighttoward pixel #2 at time t₁, and a corresponding return signal from pixel#2 may be received at a subsequent time t₂. The detector field of viewmay be aligned with pixel #2 at time t₃, where time t₃ occurs after timet₁ (e.g., time t₃>t₁), and the time (t₃−t₁) corresponds to theround-trip time for the maximum range of the lidar system 100. If thereturn signal from pixel #2 includes scattered light from a targetlocated at the maximum range, then t₃ may be approximately equal to t₂(e.g., the light is received at approximately the same time as thedetector field of view is aligned with pixel #2). Otherwise, if thereturn signal from pixel #2 originates from a target located closer thanthe maximum range, then t₃ is greater than t₂ (e.g., the light isreceived at time t₂ before the detector field of view is substantiallyaligned with pixel #2 at time t₃).

In some embodiments, after emitting a pulse of light at a time t₁, thelight source 110 may be configured to emit another pulse of light at atime t₄. The subsequent pulse of light may be emitted at a time when thedetector field of view is aligned with pixel #2 or at a subsequent time.The detector field of view may be aligned with pixel #2 at a time t₃,where (t₃−t₁) corresponds to the round-trip time for the maximum rangeof the lidar system 100, and the light source 110 may emit thesubsequent pulse of light at time t₄, where t₄ is greater than or equalto t₃. Additionally, the pixels may include pixel #3 located adjacent topixel #2 along the scanning direction, and at time t₄ when the pulse isemitted, the field of view of the light source 110 may be aligned todirect the pulse toward pixel #3.

FIG. 9 illustrates the spatial relationship between a downrange pixeland the field of view of a detector, where the detector field of view(FOV) is larger than the pixel. In some embodiments, the angular size ofa detector field of view may be greater than the angular size of thelight-source field of view. As an example, a detector field of view maybe approximately 1.5×, 2×, 3×, 4×, 5×, or 10× larger than the size of apixel (which corresponds to the field of view of light source 110). InFIG. 9, the detector FOV is approximately 2.5 times larger than pixel #1(e.g., the diameter of the detector FOV is approximately 2.5 times thediameter of pixel #1). As another example, the divergence of thedetector FOV may be approximately 1.5×, 2×, 3×, 4×, 5×, or 10× largerthan the divergence of the light-source FOV. If the detector FOV has a3-mrad divergence and the light-source FOV has a 1-mrad divergence, thenat any particular distance from the light source 110, the detector FOVis 3 times larger than the light-source FOV. For example, at a distanceof 100 m from the light source 110, the light-source beam (whichcorresponds to pixel #1) may have a diameter of approximately 10 cm, andthe detector FOV may have a diameter of approximately 30 cm. At adistance of 200 m, the light-source beam may have a diameter ofapproximately 20 cm, and the detector FOV may have a diameter ofapproximately 60 cm.

In some embodiments, a lidar system 100 may perform a series of forwardand reverse scans. As an example, a forward scan may include thedetector FOV being scanned horizontally from left to right, and areverse scan may include the detector being scanned from right to left,or vice versa. As another example, a forward scan may include thedetector FOV being scanned vertically (e.g., scanning upward ordownward), and a reverse scan may include the detector FOV being scannedin the opposite direction. As another example, a forward scan mayinclude the detector FOV begin scanned along any suitable direction(e.g., along a 45-degree angle), and a reverse scan may include thedetector FOV being scanned along a substantially opposite direction.

As illustrated in FIG. 9, the detector FOV may be scanned along aleft-to-right direction during a forward scan, and the detector FOV maybe scanned along a right-to-left direction during a reverse scan. Insome embodiments, the forward and reverse scans may trace paths that areadjacent to or displaced with respect to one another. As an example, areverse scan may follow a line in the field of regard that is displacedabove, below, to the left of, or to the right of a previous forwardscan. As another example, a reverse scan may scan a row in the field ofregard that is displaced below a previous forward scan, and the nextforward scan may be displaced below the reverse scan. The forward andreverse scans may continue in an alternating manner with each scan beingdisplaced with respect to the previous scan until a complete field ofregard has been covered. Scans may be displaced with respect to oneanother by any suitable angular amount, such as for example, byapproximately 0.05°, 0.1°, 0.2°, 0.5°, 1°, or 2°.

In some embodiments, a lidar system 100 may be configured so that thedetector FOV is larger than the light-source FOV, and the detector andlight-source FOVs are substantially coincident or overlapped. The lightsource 110 may emit a pulse of light toward pixel #1 (e.g., when thepulse is emitted, the light-source FOV may partially, substantially, orcompletely overlap pixel #1). The FOV of a detector may be larger thanthe light-source FOV, and when the pulse of light is emitted towardpixel #1, the detector FOV may contain and may be approximately centeredon pixel #1. As illustrated in FIG. 9, the detector FOV may not have anysubstantial offset with respect to the light-source FOV, and as thepulse of light propagates to and from a target, the detector FOV scansto the right during a forward scan and to the left during a reversescan. The size of the pixel #1 and the detector FOV may be configured sothat during a forward or reverse scan, the detector FOV maysubstantially contain pixel #1 at least until a round-trip timecorresponding to the maximum range of the lidar system has elapsed. Whenthe round-trip time corresponding to the maximum range of the lidarsystem has elapsed, the detector FOV may have moved so that the pixel #1is located at or near the left or right edge of the detector FOV. Forexample, during a forward scan, after the round-trip time correspondingto the maximum range has elapsed, the left edge of pixel #1 may besubstantially coincident with the left edge of the detector FOV.

FIG. 10 is a diagram of a detector array 128 which includes twodetectors 130 g, 130 h. In some embodiments, a lidar system 100 mayinclude a detector array 128 with a first detector 130 g and a seconddetector 130 h. As an example, each of the detectors 130 g and 130 h maybe an avalanche photodiode (APD) or a single-photon avalanche diode(SPAD). As another example, each of the detectors 130 g and 130 h may bea PN photodiode (e.g., a photodiode structure formed by a p-typesemiconductor and a n-type semiconductor) or a PIN photodiode (e.g., aphotodiode structure formed by an undoped intrinsic semiconductor regionlocated between p-type and n-type regions). The detectors 130 g, 130 hmay each have an active region or an avalanche-multiplication regionthat includes silicon, germanium, or InGaAs. The active region oravalanche-multiplication region may have any suitable size, such as forexample, a diameter or width of approximately 50-500 μm.

FIG. 11 illustrates forward and reverse scans based on the detectorarray in FIG. 10. In some embodiments, a lidar system 100 may include alight source 110, a scanner 118, and a detector array 128 with twodetectors 130 g, 130 h. The two detectors 130 g and 130 h may be offsetfrom one another along a direction corresponding to the light-sourcescanning direction, and the field of view of the light source 110 may belocated between the FOVs of detectors 130 g and 130 h. The scanner 118may be configured to scan the light-source FOV (as well as the FOVs ofdetectors 130 g and 130 h) in a forward-scanning direction and in areverse-scanning direction across multiple pixels located downrange fromthe lidar system. As an example, the scanner 118 may scan thelight-source FOV (and the detector FOVs) along the forward-scanningdirection, and then the scanner 118 may reverse direction and make asubsequent scan along the reverse-scanning direction. As discussedherein, forward and reverse scans may trace paths that are adjacent toor displaced with respect to one another. The forward and reverse scansmay be performed alternately with each reverse scan displaced withrespect to the previous forward scan, and each forward scan displacedwith respect to the previous reverse scan. As an example, a forward scanmay follow a substantially horizontal path, and for the subsequentreverse scan, the scanner 118 may deflect the light-source FOV (as wellas the FOVs of detectors 130 g and 130 h) vertically by some angle(e.g., 0.5°).

In FIG. 11, the forward scan traces across pixel #1 horizontally fromleft to right, and the reverse scan traces from right to left acrosspixel #2, which is located below pixel #1. In some embodiments, thefield of view of detector 130 g may be offset from the light-sourcefield of view in a direction opposite the forward-scanning direction(which corresponds to the reverse-scanning direction), and the field ofview of detector 130 h may be offset from the light-source field of viewin the forward-scanning direction. In the forward scan illustrated inFIG. 11, the FOV of detector 130 h leads the light-source FOV(corresponding to pixel #1), and the FOV of detector 130 g lags behindthe light-source FOV. In the reverse scan, the relative orientation ofthe detectors is interchanged so that the FOV of detector 130 g leadsthe light-source FOV (corresponding to pixel #2), and the FOV ofdetector 130 h lags behind the light-source FOV. In some embodiments,during a forward scan, the lidar system 100 may use a signal fromdetector 130 g to determine a distance to a target, and during a reversescan, the lidar system 100 may use a signal from detector 130 h todetermine a distance to a target. In some embodiments, a signalgenerated by detector 130 h may be disregarded during a forward scan,and a signal generated by detector 130 g may be disregarded during areverse scan.

In some embodiments, during a forward scan, the light source 110 mayemit a pulse of light, and the scanner 118 may direct the pulse of lighttoward pixel #1. When the pulse is emitted, the FOVs of detector 130 gand 130 h may each overlap less than or equal to 20% of pixel #1. Thescanner 118 may scan the FOVs of detector 130 g and 130 h along theforward-scanning direction (e.g., left to right in FIG. 11), anddetector 130 g may detect a portion of the pulse of light which isscattered by a target located downrange from the lidar system 100. Astime progresses, the overlap of detector 130 h FOV with pixel #1 maydecrease until there is no overlap, and the overlap of detector 130 gFOV with pixel #1 may increase until it reaches a maximum overlap (e.g.,greater than or equal to 80% overlap). The maximum overlap betweendetector 130 g FOV and pixel #1 may occur at a time that corresponds tothe maximum range of the lidar system, and after that, the overlapbetween detector 130 g FOV and pixel #1 may decrease as the forward scancontinues.

In some embodiments, during a reverse scan, the light source 110 mayemit another pulse of light, and the scanner 118 may direct the pulse oflight toward pixel #2. When the pulse is emitted, the FOVs of detector130 g and 130 h may each overlap less than or equal to 20% of pixel #2.The scanner 118 may scan the FOVs of detector 130 g and 130 h along thereverse-scanning direction (e.g., right to left in FIG. 11), anddetector 130 h may detect a portion of the pulse of light which isscattered by a target located downrange from the lidar system 100. Astime progresses, the overlap of detector 130 g FOV with pixel #2 maydecrease until there is no overlap, and the overlap of detector 130 hFOV with pixel #2 may increase until it reaches a maximum overlap (e.g.,greater than or equal to 80% overlap). The maximum overlap betweendetector 130 h FOV and pixel #2 may occur at a time that corresponds tothe maximum range of the lidar system, and after that, the overlapbetween detector 130 h FOV and pixel #2 may decrease as the reverse scancontinues.

In some embodiments, a detector array 128 may include two detectors(e.g., a first detector and a second detector), where the first detectoris used to detect scattered light during a forward scan, and the seconddetector is used to detect scattered light during a reverse scan. Thelidar system 100 may include an optical element configured to directscattered light to the first detector during the forward scan and todirect scattered light to the second detector during the reverse scan.As an example, the scanner 118 may be used to apply a first amount offixed deflection or angular offset during a forward scan so thatscattered light from an emitted pulse is directed to the first detector.Similarly, the scanner 118 may apply a second amount of deflection orangular offset during a reverse scan so that scattered light is directedto the second detector. As another example, the lidar system 100 mayinclude an additional deflection mirror or a deflecting element (e.g., awedged optic) that has two deflection states for directing scatteredlight to the first or second detector during a forward or reverse scan,respectively. In some embodiments, a lidar system may include onedetector configured to detect scattered light during both forward andreverse scans. The lidar system 100 may include an optical element thatprovides two states for the orientation of the detector FOV. During aforward scan, the detector FOV may be oriented so that it lags the lightsource FOV and detects scattered light from emitted pulses, and during areverse scan, the detector FOV may be oriented so that it also lags thelight source FOV.

In some embodiments, a lidar system 100 may include a light source 110,a splitter 120, a scanner 118, and a detector array 128. The lightsource 110 may emit pulses of light, and the splitter 120 may split eachemitted pulse of light into two or more pulses of angularly separatedlight. The pulses may be separated by any suitable angle Θ, such as forexample, 1 mrad, 2 mrad, 5 mrad, 10 mrad, 20 mrad, or 50 mrad. Thescanner 118 may scan pulses of light, which are emitted by the lightsource 110 and split by the splitter 120, along a scanning directionacross pixels located downrange from the lidar system 100. The detectorarray 128 may include two or more detectors. As an example, the splitter120 may split an emitted pulse into two pulses of angularly separatedlight (e.g., a first pulse and a second pulse), and the detector array128 may include a first detector 130 a and a second detector 130 b. Thefirst and second detectors may be separated by a detector-separationdistance along a direction corresponding to the scanning direction ofthe light pulses. The first detector may be configured to detectscattered light from the first pulse of light, and the second detectormay be configured to detect scattered light from the second pulse oflight. In some embodiments, the lidar system 100 may also include aprocessor configured to determine one or more distances to one or moretargets based at least in part on a time of flight of the first pulse oflight or a time of flight of the second pulse of light.

In some embodiments, the splitter 120 may include a holographic opticalelement, a diffractive optical element, a polarizing beam splitter, anon-polarizing beam splitter, or a beam splitter with a metallic ordielectric coating. As an example, the splitter 120 may include a beamsplitter that is manufactured using a holographic process, or thesplitter 120 may include a diffractive beam splitter. As anotherexample, the splitter 120 may include a holographic element or adiffractive element that divides an input beam into two or more outputbeams. In some embodiments, the splitter 120 may be positioned after thescanner 118 so that the splitter 120 receives the emitted pulses oflight from the scanner 118. As illustrated in FIG. 1, the scanner 118receives pulses of light emitted by the light source 110, and thesplitter 120 is positioned after the scanner 118 to receive the pulsesfrom the scanner 118. In some embodiments, the scanner 118 may bepositioned after the splitter 120 so that the splitter 120 receivespulses of light emitted by the light source 110, and the scanner 118receives pulses of light after they are split by the splitter 120.

In some embodiments, the splitter 120 may be configured to split a pulseof light substantially equally into two pulses. As an example, thesplitter 120 may receive one pulse of light and split it into a firstpulse and a second pulse, where the first and second pulses each haveapproximately one-half of the energy or peak power of the received pulseof light. In some embodiments, the splitter 120 may be configured tosplit a pulse of light into three pulses of angularly separated light(e.g., a first pulse, a second pulse, and a third pulse). Additionally,the detector array may include three detectors (e.g., a first detector,a second detector, and a third detector), where each detector isconfigured to receive and detect light from one of the respective pulsesof light (e.g., the first detector detects light from the first pulse).In some embodiments, the angularly separated pulses of light from thesplitter 120 may be split along a direction corresponding to thescanning direction. As an example, if the scanning direction issubstantially horizontal, the angularly separated pulses of light mayalso be split along the same horizontal direction.

In some embodiments, the light source 110 may emit a pulse of light at atime t₁, and the splitter 120 may split the pulse into two pulses (e.g.,a first pulse and a second pulse). The scanner 118 may scan a firstlight-source field of view associated with the first pulse and a secondlight-source field of view associated with the second pulse along thescanning direction and across the pixels located downrange from thelidar system 100. The pixels may include pixel #1, pixel #2, pixel #3,pixel #4, and pixel #5 positioned in order along the scanning direction(e.g., the first or second light-source field of view may scan acrossthe pixels and encounter the pixels in the following order: pixel #1,pixel #2, pixel #3, pixel #4, and pixel #5). In some embodiments, thescanner 118 may direct the first pulse of light toward pixel #2 and thesecond pulse of light toward pixel #5. Additionally, the scanner 118 mayscan a field of view of the first detector and a field of view of thesecond detector along the scanning direction across the pixels. Thefirst-detector field of view may be offset from the first light-sourcefield of view in a direction opposite the scanning direction, where, attime t₁, the first-detector field of view at least partially overlapsthe first pixel, and the first light-source field of view at leastpartially overlaps the second pixel. Similarly, the second detectorfield of view may be offset from the second light-source field of viewin a direction opposite the scanning direction, where, at time t₁, thesecond detector field of view at least partially overlaps the fourthpixel, and the second light-source field of view at least partiallyoverlaps the fifth pixel.

In some embodiments, the separation distance between the first andsecond pulses of light at the maximum range of the lidar system 100 maycorrespond to the separation distance between detectors 130 a and 130 b.As an example, when the first and second pulses of light are incident ona target located at the maximum range of the lidar system 100, the firstand second pulses of light may be separated by a distance thatcorresponds to the detector-separation distance. When the first andsecond pulses of light are emitted, their fields of view may overlappixels #2 and #5, respectively. When the first and second pulses oflight return to the lidar system 100 after scattering from the target,the first-detector field of view may overlap pixel #2, and the seconddetector field of view may overlap pixel #5. In some embodiments, theseparation distance between the first and second pulses of light at themaximum range of the lidar system 100 may correspond to an odd number ofpixels greater than or equal to three pixels. As an example, at themaximum range, the first and second pulses of light may be separated bya distance corresponding to three pixels so that when the first pulse isdirected at pixel #2, the second pulse is directed at pixel #5. In someembodiments, the detector-separation distance may correspond to an oddnumber of pixels greater than or equal to three pixels. As an example,the detector-separation distance may correspond to three pixels so thatwhen the first detector receives light from pixel #2, the seconddetector receives light from pixel #5.

FIG. 12 is a diagram of a detector array 128 which includes threedetectors 130 i, 130 j, and 130 k. Each of the detectors 130 i, 130 j,and 130 k may be an APD or a SPAD. In some embodiments, a lidar system100 may include a light source 110, a scanner 118, a splitter 120, and adetector array 128 with three detectors 130 i, 130 j, and 130 k. Thethree detectors 130 i, 130 j, 130 k may be separated from one another bya detector-separation distance along a direction corresponding to thelight-source scanning direction.

FIG. 13 illustrates forward and reverse scans based on the detectorarray in FIG. 12. During a forward scan, the splitter 120 may split anemitted pulse into two pulses of angularly separated light (e.g., afirst pulse and a second pulse which are directed to pixel #1 and pixel#2, respectively). When the pulse is emitted, the field of view of thefirst pulse (corresponding to pixel #1) may be located between the FOVsof detectors 130 i and 130 j, and the field of view of the second pulse(corresponding to pixel #2) may be located between the FOVs of detectors130 j and 130 k. The detector 130 i FOV may lag the FOV of the firstpulse, and detector 130 i may be configured to detect scattered lightfrom the first pulse. Similarly, the detector 130 j FOV may lag the FOVof the second pulse, and detector 130 j may be configured to detectscattered light from the second pulse. Additionally, during a forwardscan, the signal from detector 130 k may be ignored. In someembodiments, there may be additional pixels (not illustrated in FIG. 13)located between pixels #1 and #2 (and additional pixels located betweenpixels #3 and #4).

In some embodiments, the scanner 118 may be configured to scanadditional pulses of light, which are emitted by the light source 110and split by the splitter 120, along a reverse-scanning directioncorresponding to the direction opposite the forward-scanning direction.The light source 110 may emit an additional pulse of light while thescanner 118 is scanning in the reverse-scanning direction. As discussedherein, scans of the reverse-scanning direction may be displaced withrespect to the forward-scanning direction. In FIG. 13, the forward scantraces across pixels #1 and #2, and the reverse scan traces acrosspixels #3 and #4, which are located below pixels #1 and #2. The splitter120 may split the emitted pulse into a third pulse of light and a fourthpulse of light, which are angularly separated. The third pulse may bedirected to pixel #3, and the fourth pulse may be directed to pixel #4.When the pulse is emitted, the field of view of the third pulse(corresponding to pixel #3) may be located between the FOVs of detectors130 j and 130 k, and the field of view of the second pulse(corresponding to pixel #4) may be located between the FOVs of detectors130 i and 130 j. During a reverse scan, the detector 130 k FOV may lagthe FOV of the third pulse, and detector 130 k may be configured todetect scattered light from the third pulse. Similarly, the detector 130j FOV may lag the FOV of the fourth pulse, and detector 130 j may beconfigured to detect scattered light from the fourth pulse.Additionally, during a reverse scan, the signal from detector 130 i maybe ignored.

A lidar system 100 as described or illustrated herein may also includevarious elements described or illustrated in U.S. Provisional PatentApplication No. 62/243,633, filed 19 Oct. 2015 and entitled “LidarSystem with Improved Signal-to-Noise Ratio in the Presence of SolarBackground Noise” or U.S. Provisional Patent Application No. 62/261,214,filed 30 Nov. 2015 and entitled “Lidar System with a Distributed Laserand a Plurality of Sensor Heads,” each of which is incorporated hereinby reference.

FIG. 14 illustrates an example method 400 for detecting light scatteredby a target. The method may begin at step 410, where a light source 110of a lidar system 100 emits a pulse of light at a time t₁. At step 420,a field of view of the light source 110 may be scanned in aforward-scanning direction across multiple pixels located downrange fromthe lidar system 100. The pixels may include a first pixel and a secondpixel, where the second pixel is located adjacent to the first pixelalong the forward-scanning direction. At step 430, the pulse of lightmay be directed toward the second pixel. At step 440, a field of view ofa first detector of the lidar system 100 may be scanned. Thefirst-detector field of view may be scanned in the forward-scanningdirection across the pixels. Additionally, the first-detector field ofview may be offset from the light-source field of view in a directionopposite the forward-scanning direction, where, at time t₁, thefirst-detector field of view at least partially overlaps the firstpixel, and the light-source field of view at least partially overlapsthe second pixel. At step 450, a portion of the pulse of light scatteredby a target located at least partially within the second pixel may bedetected, at which point the method may end. The portion of the pulse oflight may be detected at a time t₂, where t₂ is greater than t₁.

FIG. 15 illustrates an example method 500 for detecting scattered lightfrom angularly separated pulses of light. The method may begin at step510, where a light source 110 of a lidar system 100 emits a pulse oflight. At step 520, the emitted pulse of light may be split into two ormore pulses of angularly separated light. The two or more pulses may besplit by a splitter 120 and may include a first pulse of light and asecond pulse of light. At step 530, pulses of light (which are emittedby the light source 110 and split by the splitter 120) may be scannedalong a scanning direction across pixels located downrange from thelidar system 100. At step 540, scattered light from the first pulse oflight may be detected. At step 550, scattered light from the secondpulse of light may be detected, at which point the method may end. Thescattered light from the first and second pulses of light may bedetected by a first detector and a second detector, respectively, wherethe first and second detectors are part of a detector array. The firstand second detectors may be separated by a detector-separation distancealong a direction corresponding to the scanning direction of the lightpulses.

Embodiments have been described in connection with the accompanyingdrawings. However, it should be understood that the figures are notdrawn to scale. Distances, angles, etc. are merely illustrative and donot necessarily bear an exact relationship to actual dimensions andlayout of the devices illustrated. In addition, the foregoingembodiments have been described at a level of detail to allow one ofordinary skill in the art to make and use the devices, systems, etc.described herein. A wide variety of variation is possible. Components,elements, and/or steps may be altered, added, removed, or rearranged.While certain embodiments have been explicitly described, otherembodiments will become apparent to those of ordinary skill in the artbased on this disclosure.

The systems and methods described herein can advantageously beimplemented, at least in part, using computer software, hardware,firmware, or any combination of software, hardware, and firmware.Software modules can comprise computer executable code for performingthe functions described herein. In some embodiments, computer-executablecode is executed by one or more general purpose computers. However, askilled artisan will appreciate, in light of this disclosure, that anymodule that can be implemented using software to be executed on ageneral purpose computer can also be implemented using a differentcombination of hardware, software, or firmware. For example, such amodule can be implemented completely in hardware using a combination ofintegrated circuits. Alternatively or additionally, such a module can beimplemented completely or partially using specialized computers designedto perform the particular functions described herein rather than bygeneral purpose computers. In addition, where methods are described thatare, or could be, at least in part carried out by computer software, itshould be understood that such methods can be provided oncomputer-readable media (e.g., optical disks such as CDs or DVDs, harddisk drives, flash memories, diskettes, or the like) that, when read bya computer or other processing device, cause it to carry out the method.

While certain embodiments have been explicitly described, otherembodiments will become apparent to those of ordinary skill in the artbased on this disclosure. Therefore, the scope of the invention isintended to be defined by reference to the claims and not simply withregard to the explicitly described embodiments.

What is claimed is:
 1. A lidar system comprising: a light sourceconfigured to emit a pulse of light; a splitter configured to split theemitted pulse of light into two or more pulses of angularly separatedlight comprising a first pulse of light and a second pulse of light; ascanner configured to scan pulses of light, which are emitted by thelight source and split by the splitter, along a scanning directionacross a plurality of pixels located downrange from the lidar system;and a detector array comprising a first detector and a second detector,wherein: the first and second detectors are separated by adetector-separation distance along a direction corresponding to thescanning direction of the light pulses; the first detector is configuredto detect scattered light from the first pulse of light; and the seconddetector is configured to detect scattered light from the second pulseof light.
 2. The lidar system of claim 1, wherein: the scanner beingconfigured to scan the pulses of light comprises the scanner beingconfigured to scan a first light-source field of view associated withthe first pulse and a second light-source field of view associated withthe second pulse along the scanning direction across the plurality ofpixels; and the plurality of pixels comprises a first pixel, a secondpixel, a third pixel, a fourth pixel, and a fifth pixel positioned alongthe scanning direction, wherein the first or second light-source fieldof view scans across the plurality of pixels and encounters the pixelsin an order as follows: first pixel, second pixel, third pixel, fourthpixel, fifth pixel.
 3. The lidar system of claim 2, wherein the pulse oflight is emitted at a time t₁ and the scanner is further configured to:direct the first pulse of light toward the second pixel; direct thesecond pulse of light toward the fifth pixel; and scan a field of viewof the first detector and a field of view of the second detector alongthe scanning direction across the plurality of pixels, wherein: thefirst-detector field of view is offset from the first light-source fieldof view in a direction opposite the scanning direction, wherein, at timet₁: the first-detector field of view at least partially overlaps thefirst pixel; and the first light-source field of view at least partiallyoverlaps the second pixel; and the second detector field of view isoffset from the second light-source field of view in the directionopposite the scanning direction, wherein, at time t₁: the seconddetector field of view at least partially overlaps the fourth pixel; andthe second light-source field of view at least partially overlaps thefifth pixel.
 4. The lidar system of claim 1, further comprising aprocessor configured to determine one or more distances to one or moretargets based at least in part on a time of flight of the first pulse oflight or a time of flight of the second pulse of light.
 5. The lidarsystem of claim 1, wherein the scanner is configured to receive thefirst and second pulses of light from the splitter.
 6. The lidar systemof claim 1, wherein the splitter is configured to receive the emittedpulse of light from the scanner.
 7. The lidar system of claim 1, whereinthe splitter comprises a holographic element or a diffractive element.8. The lidar system of claim 1, wherein the splitter is configured tosplit the emitted pulse of light substantially equally into two pulses,wherein the first pulse of light and the second pulse of light each haveapproximately one-half of the energy or peak power of the emitted pulseof light.
 9. The lidar system of claim 1, wherein: the splitter isconfigured to split the emitted pulse of light into three pulses ofangularly separated light; the angularly separated pulses of lightfurther comprise a third pulse; and the detector array further comprisesa third detector configured to detect scattered light from the thirdpulse of light.
 10. The lidar system of claim 1, wherein the angularlyseparated pulses of light are split along a direction corresponding tothe scanning direction.
 11. The lidar system of claim 1, wherein aseparation distance between the first and second pulses of light at amaximum range of the lidar system corresponds to the detector-separationdistance.
 12. The lidar system of claim 1, wherein a separation distancebetween the first and second pulses of light at a maximum range of thelidar system corresponds to an odd number of pixels greater than orequal to three pixels.
 13. The lidar system of claim 1, wherein thedetector-separation distance corresponds to an odd number of pixelsgreater than or equal to three pixels.
 14. The lidar system of claim 1,wherein the scanner is further configured to scan additional pulses oflight, which are emitted by the light source and split by the splitter,along a reverse-scanning direction corresponding to a direction oppositethe scanning direction.
 15. The lidar system of claim 14, wherein: thelight source is further configured to emit an additional pulse of lightwhile the scanner is scanning in the reverse-scanning direction; thesplitter is further configured to split the additional pulse of lightinto a third pulse of light and a fourth pulse of light, which areangularly separated; and the detector array further comprises a thirddetector, wherein: the second detector is configured to detect scatteredlight from the fourth pulse of light; and the third detector isconfigured to detect scattered light from the third pulse of light. 16.The lidar system of claim 15, wherein the second and third detectors areseparated by the detector-separation distance along the directioncorresponding to the scanning direction of the light pulses.
 17. Amethod comprising: emitting, by a light source of a lidar system, apulse of light; splitting, by a splitter, the emitted pulse of lightinto two or more pulses of angularly separated light comprising a firstpulse of light and a second pulse of light; scanning pulses of light,which are emitted by the light source and split by the splitter, along ascanning direction across a plurality of pixels located downrange fromthe lidar system; detecting, by a first detector of a detector array,scattered light from the first pulse of light, wherein the detectorarray comprises the first detector and a second detector, wherein thefirst and second detectors are separated by a detector-separationdistance along a direction corresponding to the scanning direction ofthe light pulses; and detecting, by the second detector of the detectorarray, scattered light from the second pulse of light.
 18. The method ofclaim 17, further comprising determining one or more distances to one ormore targets based at least in part on a time of flight of the firstpulse of light or a time of flight of the second pulse of light.
 19. Themethod of claim 17, further comprising scanning additional pulses oflight, which are emitted by the light source and split by the splitter,along a reverse-scanning direction corresponding to a direction oppositethe scanning direction.
 20. The method of claim 19, further comprising:emitting, by the light source, an additional pulse of light while thescanner is scanning in the reverse-scanning direction; splitting, by thesplitter, the additional pulse of light into a third pulse of light anda fourth pulse of light, which are angularly separated; detecting, bythe second detector, scattered light from the fourth pulse of light; anddetecting, by a third detector of the detector array, scattered lightfrom the third pulse of light.